In conventional rectangular balers, crop material is picked up from the ground by a pick-up unit and fed into an elongated bale case or chamber. The crop material is fed into the bale case in timed sequence with a reciprocating plunger. The plunger compresses the crop material, gradually forming a bale and advancing it toward a exit opening in the bale case. When the bale being formed reaches a desired length, a tying mechanism is actuated to wrap at least one loop of binding material around the bale, tie a knot in the binding material, and cut the tied loop from the supply of binding material. This tying operation leaves an end portion of the binding material from the supply so that it extends across the bale case. After the tying operation, the formation of a new bale begins and as the new bale is formed it forces the tied bale and a portion of the binding material toward the exit opening in the bale case, the binding material sliding between the tied bale and the new bale being formed as both are forced to move toward the exit opening.
As disclosed in Pat. No. 4,624,180, a baler of the type described above may have its operations automatically controlled by a microprocessor. In addition, an operator may input information into a control panel so that the baler automatically forms bales compacted to a desired density.
When baling damp silage crop at a desired density, the tying process may intermittently fail. Failure occurs either because of breakage of the binding material or because the binding material is pulled from the tying mechanism. Both types of failure usually occur within a few plunger strokes after a cycle of the tying mechanism. It is during this interval that the binding material encounters the greatest resistance to sliding between the tied bale and the new bale being formed as both are pushed toward the exit opening in the bale case. Copending application Ser. No. 07/338,175 discloses a method whereby failures of the tying process can be substantially reduced by operating the density control mechanism so that for the first few strokes of the plunger after each bale is tied, the incoming crop material is compacted to a lower density.
The method disclosed in the copending application substantially reduces the number of failures of the tying process. However, when working a very light windrow, or when a cycle of the tying mechanism takes place near the end of a windrow as the baler enters the headlands, failure of the tying process may still occur. The reason is that during several plunger strokes following a cycle of the tying mechanism little crop material enters the bale case. Thus, after the several plunger strokes, when the density control returns to the higher (normal) density, conditions in the baler are almost the same as immediately after a cycle of the tying mechanism. When crop material is then compacted at the higher density, the binding material may still break.